Add tests for Horizontal/Vertical(Scroll) containers.

tests/snapshot_tests/snapshot_apps/layout_containers.py

@@ -0,0 +1,56 @@
+"""
+App to test layout containers.
+"""
+
+from typing import Iterable
+
+from textual.app import App, ComposeResult
+from textual.containers import (
+    Grid,
+    Horizontal,
+    HorizontalScroll,
+    Vertical,
+    VerticalScroll,
+)
+from textual.widget import Widget
+from textual.widgets import Button, Input, Label
+
+
+def sub_compose() -> Iterable[Widget]:
+    yield Button.success("Accept")
+    yield Button.error("Decline")
+    yield Input()
+    yield Label("\n\n".join([str(n * 1_000_000) for n in range(10)]))
+
+
+class MyApp(App[None]):
+    CSS = """
+    Grid {
+        grid-size: 2 2;
+        grid-rows: 1fr;
+        grid-columns: 1fr;
+    }
+    Grid > Widget {
+        width: 100%;
+        height: 100%;
+    }
+    Input {
+        width: 80;
+    }
+    """
+
+    def compose(self) -> ComposeResult:
+        with Grid():
+            with Horizontal():
+                yield from sub_compose()
+            with HorizontalScroll():
+                yield from sub_compose()
+            with Vertical():
+                yield from sub_compose()
+            with VerticalScroll():
+                yield from sub_compose()
+
+
+app = MyApp()
+if __name__ == "__main__":
+    app.run()